However, evidence has been mixed on whether there is a link between testosterone levels and depression, and whether testosterone treatment could help with mood disorders in at least some cases. At present it is not recommended as a treatment for depression by the UK health watchdog, Nice.

“We wanted really to clear up the picture and try to find out what is really going on, and is testosterone something that might be one day interesting for clinicians for treatment of depressive disorders or not,” said Dr Andreas Walther, a co-author of the research, from the German university TU Dresden.

Writing in the journal Jama Psychiatry, Walther and colleagues report how they carried out a review of 27 randomised control trials conducted since 2000 involving a total of 1,890 men. While some of the studies looked at men with a testosterone deficiency, others looked at men without the problem. Not all the studies involved men with a diagnosis of a depressive disorder, with some considering instead symptoms of depression, while some participants were undergoing treatment with established antidepressants or therapy.

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The team found a clear improvement in depressive symptoms among men given testosterone compared with those who did not have the treatment.

Further, the results from seven of the studies with necessary data revealed that, compared with a placebo, the chances of participants having a 50% or greater reduction in depression symptoms improved by 130% when testosterone treatment was given – a result the team say is on a par with the efficacy of established antidepressants.

The team also found that whenever the dosage of testosterone was at least 0.5g per week and the variation in symptoms between participants was low, the treatment was linked to significant reductions in depressive symptoms.

They add that it would appear benefits can be seen within six weeks of beginning the treatment, and that both younger and older men could experience mood improvements. They say the review did not show that the benefits were confined to men who had a testosterone deficiency to begin with or who had a particular severity of depression.

The researchers caution that the studies had many differences between them that could make it difficult to compare them, and stress that more research is needed, including looking at how testosterone might compare against current antidepressants.

The review also had other limitations, including that because not all of the studies involved men with a clinical diagnosis of depression, it is not clear how clinically significant the mood improvements are.

Allan Young, of theRoyal College of Psychiatrists and a professor of mood disorders at King’s College London, who was not involved in the study, said the research opened the door for further studies, including into safety and long-term impacts of testosterone treatment, as well as studies exploring whether the approach could help women with depression.

“There is certainly a signal of benefit for depression in men,” he said, although he cautioned that men with depression should not start taking testosterone as a result of the research.

He said it was not clear whether testosterone was affecting mood itself or other factors. “With testosterone, there might be an effect on what one might think of broadly as vitality – men might feel like they have got more energy, might eat more, but that may not be accompanied by an effect on core symptoms of depression such as low mood and loss of interest.”

Young said it was important that the benefits appeared to be seen even where testosterone levels were not low to start with, and that there was no difference in the rate of drop-out between men given placebo or testosterone, suggesting the hormone treatment was acceptable.

“There aren’t an awful lot of new treatment options for depression,” he said. “Testosterone is a currently available treatment, so if it shown convincingly to be antidepressant you’d cut out a lot of the time-lag with getting it to patients.”